The present invention relates to a method of manufacturing a closed section structure, which is filled with a foam and serves as a carbody constituent used in, for example, a carbody pillar. Further, the present invention relates to a closed section manufactured by the method.
For example, a carbody center pillar adopts by preference a closed section structure obtained by overlaying a flat plate on a U-shaped cross-section material and by integrally welding both the flat plate and the U-shaped cross-section material. Filling a foam into a closed section space is known as a technique of enhancing rigidity thereof (see, for instance, Patent Document 1).
[Patent Document 1]
JP-UM-A-4-123781 (see page 5, and FIGS. 1 and 2)
FIGS. 6A to 6D are views reproduced from FIGS. 1 and 2 of JP-UM-A-4-123781. Incidentally, FIGS. 2 and 1 thereof are put together into a set of FIGS. 6A to 6D and arranged in this order. Additionally, reference characters are reassigned to constituent elements, respectively.
In a stage shown in FIG. 6A, an aluminum plate 102 indicated by an imaginary line is put on a lower die 101. Then, press molding is performed thereon by a punch 103. Thus, an outer panel 104 indicated by solid lines is obtained. This outer panel 104 is left attached to the lower die 101.
As shown in FIG. 6B, a foamed aluminum block 105 is put on the outer panel 104. The foamed aluminum block 105 is compressed by a punch 106.
Consequently, as shown in FIG. 6C, a compressed foam 107 can be filled into a concave portion of the outer panel 104.
Then, as shown in FIG. 6D, a flat-plate-like inner panel 108 is put thereon. Subsequently, flanges of the panels 104 and 108 are spot-welded to each other, so that these panels are integrated with each other. Consequently, a center pillar 109, whose closed section space is filled with the foam 107, can be obtained.
Although the inner section of the aforementioned center pillar 109 is a simple rectangular one, most of those of actual carbody constituents, such as a center pillar, are complicated closed sections, such as polygonal ones, due to necessity of design thereof or the like.
There are two possible methods of manufacturing carbody constituents respectively having complicated closed sections. One is a “postprocessing method” of additionally performing press working on the center pillar 109, which is rectangular cross sectionally shaped and obtained in the stage shown in FIG. 6D. The other is a “concurrent processing method” of shaping the outer panel 104 and the foamed aluminum block 105 in the stages illustrated in FIGS. 6A to 6C in such a way as to have complicated section shapes.
According to the postprocessing method, the filled foam 107 may come off the outer panel 104 to thereby generate a space therein. The generation of a space makes it impossible to desirably increase the rigidity of carbody constituents.
According to the concurrent processing method, there is no such fear. However, there is the necessity for preliminarily shaping the foamed aluminum block 105 in such a manner as to have a complicated section. Thus, the manufacturing cost thereof runs up.